http://www.cic.gc.ca/english/resources/tools/temp/visa/validity/implied.asp
You can show them this link which is on the website of cic itself.
And I quote from the link:
A temporary resident must apply to extend their period of authorized stay before it ends. If they have done so, their period of authorized stay as a temporary resident is extended by law until a decision is made [R183(5)]. Such a person is considered to have implied status as a temporary resident during that period.
If a temporary resident applies for renewal of their work or study permit and their permit expires before a decision is made, R186(u) and R189 (the right to continue working or studying under the same conditions pending a determination of their application for renewal) apply only as long as the person remains in Canada.
So this means you can keep working under the same conditions of your expired permit, given that the OWP application has been received by CIC before your current work permit expired.
I had the same issue with my employer but was able to keep working because of this rule and received my OWP without issues, on which it was also stated that I had maintained my status as a temporary resident under my previous conditions of the expired permit.